The present invention relates to a grease composition for constant velocity joints and in particular to a grease composition for fixed type constant velocity joints of motorcars and a grease composition for sliding type constant velocity joints of motorcars. More particularly, the present invention pertains to a grease composition for constant velocity joints, which can efficiently lubricate portions of the joint which are easily worn out and are liable to generate abnormal vibrations or the like; can effectively reduce any friction; can suppress any vibration; and can improve the useful life of the joint.
In the field of motorcars, FF cars have rapidly increased and functional 4WD cars have likewise increased from the viewpoint of the reduction in the weight of cars and the insurance of the accommodation space thereof and accordingly, there have widely been used constant velocity joints (CVJ). FIG. 1 shows an embodiment of a Rzeppa type joint used as a fixed type constant velocity joint, among these CVJ""s. In this Rzeppa type joint, when the joint transmits a running torque while it has a working angle, more severer lubricating conditions have been required for the fitting position of track grooves 2 of an outside wheel 1, track grooves 4 of an inside wheel 3 and balls 5, as the generating power of cars have been increased, cars have been driven at a higher speed and CVJ""s have been lighter and smaller. For this reason, the conventionally used grease compositions such as a lithium-containing extreme-pressure grease, which contains a sulfur-phosphorus-containing extreme-pressure additive and a lithium-containing extreme-pressure grease, which comprises molybdenum disulfide are insufficient in the durability. Moreover, it has been required to improve the heat resistance of these grease compositions.
FIG. 2 shows an embodiment of a double offset joint (DOJ) used as a sliding type joint. In this DOJ, when the joint transmits a running torque, while it has a working angle, the joint undergoes complicated rolling and sliding motions at the fitting position of track grooves 3 of an outside wheel 1, track grooves 4 of an inside wheel 2 and balls 5, and the frictional resistance in the sliding portions of the joint generates a force in the axial direction. This force is referred to as xe2x80x9can induced thrust forcexe2x80x9d. This DOJ is provided with the track grooves 3 on the internal face of the outside wheel 1 at intervals of 60 degrees and accordingly, the induced thrust force is generated 6 times per revolution.
If the cycle of such induced thrust forces is in agreement with the natural frequencies of, for instance, an engine, a car body and/or a suspension, a resonance of the car body is induced and this gives a disagreeable impression to the occupants of the car. Therefore, it is desirable to reduce the foregoing induced thrust force to a level of as low as possible. In a packaged motorcar, inconvenience such as beating and stuffy sounds is generated during high speed travelling of the car due to the. resonance.
The conventional lithium-containing extreme-pressure grease, which contains a sulfur-phosphorus-containing extreme-pressure additive, and a lithium-containing extreme-pressure grease, which comprises molybdenum disulfide, suffer from a problem concerning the vibration resistance. In addition, Japanese Un-Examined Patent Publication No. Sho 62-207397 discloses an extreme-pressure grease, which comprises, as an essential component, a sulfur-phosphorus-containing extreme-pressure additive comprising a combination of a molybdenum sulfurized dialkyl dithiocarbamate and at least one member selected from the group consisting of sulfurized fats and oils, sulfurized olefins, tricresyl phosphate, trialkyl phosphates and zinc dialkyl dithiophosphates. However, the extreme-pressure grease composition disclosed in this patent is still insufficient in the quietness.
Accordingly, it is an object of the present invention to provide a grease composition for constant velocity joints, which can efficiently lubricate such a constant velocity joint when it is applied to sides thereof to be lubricated, can efficiently inhibit any wear and is excellent in heat resistance and durability.
It is a further object of the present invention to provide a grease composition for constant velocity joints, which shows a high ability of reducing any induced thrust force and is excellent in the durability.
The inventors of this invention have conducted various intensive studies to solve the foregoing problems associated with the conventional grease compositions, have found that the foregoing objects of the present invention can effectively be achieved by the use of a specific combination of compounds and thus have completed the present invention.
According to the present invention, there is provided a grease composition for constant velocity joints, which comprises the following components:
(a) a base oil;
(b) a diurea type thickening agent represented by the following formula (1):
R1NHxe2x80x94COxe2x80x94NHxe2x80x94C6H4xe2x80x94pxe2x80x94CH2xe2x80x94C6H4xe2x80x94pxe2x80x94NHxe2x80x94COxe2x80x94NHR2xe2x80x83xe2x80x83(1)
(in the formula (1), R1 and R2 may be the same or different from one another and each represents an aryl group or a cycloalkyl group having 6 or 7 carbon atoms);
(c) a molybdenum sulfurized dialkyl dithiocarbamate;
(d) a molybdenum sulfurized dialkyl dithiophosphate;
(e) molybdenum disulfide;
(f) a calcium salt of an alkylaromatic sulfonic acid; and
(g) a phosphorus free-and sulfur-containing extreme-pressure additive.